What happens during withdrawal?
What happens physically during withdrawal? There's plenty of information about the symptoms, but nowhere does it explain what actually happens or why these symptoms occur. The only thing mentioned is that the metabolism changes and the body lacks the substance. But that doesn't explain why such extreme symptoms can occur. Let's take, for example, severe pain—what happens physically or chemically that causes this?
It depends on what substance you take away from.
Some drugs, such as heroin, are very strong painkillers. The body of addiction feels nothing more and the pain will come back. However, the body counts pain to its normal function and has previously tried to make the synapses more sensitive so that pain works normal again. Then the pain will certainly go right through the withdrawal.
Similarly, the drug will also intervene in other places of metabolism and produce similar problems during withdrawal. Now you have to note that they can all happen simultaneously.
In the transferred sense: Imagine a three-year-old toddler at the candy stand in front of the supermarket box, which is shaped from early on on on on sugar, which now demands a candy and which the mother holds an incomparable “NO!”.
Depending on the substance and intensity of dependency, the condition then occurring lasts only a few days with tolerable symptoms (cannabis) up to weeks of agony with multiple suffering (Opiates, Benzos, Alcohol).
What is going on in detail in terms of brain or neurological terms may be read by Wikipedia if you use the right search terms.